Receiver circuits are used for both terrestrial and cable reception within televisions, digital video recorders, video cassette records, set-top box devices (such as cable and satellite tuners), frequency modulation (FM) radios, models, and other electronic devices. Some smart phones also utilize receiver circuits for television reception. In general, such receiver circuits include a tuner that selects a narrowband signal from within a wide or broad-band signal having multiple channels. The tuner includes bandpass filters, amplifiers, and mixer circuits for selecting a desired channel and for rejecting unwanted channels, noise and interference.
Television signals can be broadcast at a variety of different frequencies, including ultra-high frequency (WV), very high frequency (VHF), and high frequency (HF) frequency hands. The International Telecommunications Union (ITU) defines the UHF frequency range as encompassing electromagnetic waves between 300 MHz and 3 GHz. VHF occupies frequencies within a range from approximately 30 MHz to 300 MHz, and HF occupies frequencies within a range from approximately 3 MHz to 30 MHz.
For a conventional tracking filter, multiple bandpass filters are included to cover the range of possible frequencies, each tuned to a limited portion of the overall bandwidth of the receiver. For each filter, a large tuned impedance is desirable to minimize the noise figure; however, the tuned impedance is typically a function of the frequency and the size of the inductor, which size can limit the frequency range for the particular filter.